It is planned to study three basic problems which are fundamental to cancer clinical trials and cancer care. The three problem areas are: optimal strategies for the timing and planningof medical examinations, methods for the planning and analysis of clinicaltrials in which the endpoint is survival, but where intermediate clinicalinformation (e.g., response) is available and models for cancer prevention clinical trials. The first topic is basic to any recommendations for screening examinations. Controversies exist concerning how often individuals should be screened for nearly all the common cancer sites. The proposedtheory for choosing optimal intervals may help resolve some of these issues. The model utilizes a general utility function which is a function of the probabilities of case detection and diagnosis between intervals. The modelwill be enlarged to simultaneously include both age and chronological time andthe costs of false positive outcomes. The theory will be applied to several common cancer sites (e.g., breast, cervix, colon). The second topic relates to methods which incorporate disease markers into survival models. The incorporation of the additional data will lead to more efficient statistical procedures. In some cases, it can lead to methods for evaluating survivalbenefit without the need for randomized trials. These trials require additional considerations compared to therapeutic trials. Chief amongst these are the theories of carcinogenesis and its relation to the mode of action of the intervention. The cohort of patients who are prevalent in the promotion stageof carcinogenesis and in the pre-clinical cancer state at the time of the initiation of the trial may result in different outcomes compared to individuals who will eventually enter these states at a later time. Furthermore, compliance will be incorporated in the model as it is a key issue.